Radio navigation system



Nov. 30, 1954 G. MOUNTJOY ET Al. 2,695,997

RADIO NAVIGATION SYSTEM Filed Jan. l, 1945 5 Sheets-Sheet l ff/w@ "j fg fe f;

G. MOUNTJOY ET AL Nov. 30, 1954 RADIO NAVIGATION SYSTEM 5 Sheets-Sheet 2 Filed Jan. l, 1945 @www m 7@ N M5 9 www wh Nov. 30, 1954 G. MouNTJoY ETAL 2,695,997

RADIO NAVIGATION SYSTEM l 'f n J- c l l l L l L G. MoUNTJoY ETAL 2,695,997 RADIO NAVIGATION SYSTM 5 Sheets-Sheet 5 Nov. 30, 1954 Filed Jan. 1, 1945 NNN www 55%,. Hmm

United States Patent() RADIO NAVIGATION SYSTEM Garrard Mountioy, Manhasset, and Earl Schoenfeld, Mamaroneck, N. Y., and George D. Hulst, Jr., Upper Montclair, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application January 1, 1945, Serial No. 570,818

11 Claims. (Cl. 343-103) Our invention relates to radio navigation systems and particularly to systems of the type utilizing the time difference in the propagation of radio pulses from synchronized ground stations. p

Navigation systems of this type employ pairs of synchronized ground stations that transmit radio pulses having at the instant of radiation a xed time relation to each other. Each pair of ground stations preferably transmits pulses at its individual assigned repetition rate for the purpose of station selection. The pulses are radiated to receiving equipment located on the aircraft or ship whose position is to be determined. By means of the receiving equipment, the operator on the craft determines the time difference between the pulses from the two transmitter stations of one pair as they arrive at the receiver. Since the radio pulses travel from the ground transmitters to the receiver at a known propagation rate (i. e., at the velocity of light), it is known that the position of the craft is at some point on a line corresponding to the time difference reading. By obtaining the time dilferencc reading from a second pair of ground stations, a second line corresponding to the second time difference reading is obtained, and the intersect point of the two lines is the position of the craft. Special maps having time difference lines printed thereon for the several pairs of ground stations are provided for use with the navigation system.

In order to measure the time difference in the arrival of successive pulses from a pair of ground stations, timing marker pulses that have a known time interval between them are generated. Also, pulses having a delinite time relation to the time marker pulses are generated for the' purpose of driving or synchronizing cathode ray deliecting circuits. These deilecting circuits produce cathode ray sweep traces on which the marker pulses and/or the received ground station pulses appear.

For the purpose of selecting a particular pair of ground stations, the operator selects a particular pulse repetition rate for the driving or synchronizing pulses corresponding to the repetition period of the pulses transmitted from said pair whereby the deilecting circuits may be synchronized with the received pulses from the selected pair. of ground stations. Thus a particular pair of ground stationsis selected at the receiver apparatus by turning a station selection switch to the position indicated on the receiver panel for obtaining sweep synchronizing pulses having the same repetition period as that of the pulses being transmitted from the selected pair of ground stations. Now the received pulses from the selected pair of ground stations can be made to appear stationary on the-cathode-ray sweep or trace whereas those received from' the other pairs of ground ystations will move rapidly along the same trace'. f f

In operation, the pulses from the two transmitter stations of a selected pair ofstations (whichpulses will be referred to as A and B pulses, respectively) arek made to appear on two cathode-ray traces. The Bpulse is identified as the pulse that occurs after or follows the midpoint of 'the other pulse period. The A and B pulses are brought into alignment or coincidence by moving the A pulse along its cathode-ray sweep trace, this being done by adjusting the'starting'time of Vthev cathode-ray sweep. It is then possible to measure the time displacement of the sweep required for pulse alignment. yThis is done in one`embodiment of thepreserlt system by blanking out the portion ofthe adjustable tracegfrorn the center o f the dellectingwyave cycle and. bycounting .the `timing markers 2,695,997 Pa'tented Nov. 30, 1954 ice appearing on the remaining portion of the trace. Thus, the desired time diierence between pulses is determined. A precise determination of the time difference is made possible by so designing the system that the start of the unblanked portion of the trace is expanded.

An object of the present invention is' to provide an improved method of and means for determining the time difference between electrical pulses.

A further object of the invention is to provide improved receiving equipment for a radio navigation system of the type utilizing the propagation of radio pulses from pairs of synchronized ground stations.

A still further object of the invention is to provide an improved method of and means for indicating the time difference between radio pulses transmitted from synchronized ground stations.

A still further object of the invention is to provide an improved method of and means for obtaining a simple time marker presentation in a radio navigation system of the above-mentioned type.

The invention will be better understood from the following description taken in connection with the accompanying drawing in which Figure l is a block diagram of navigation receiving apparatus designed in accordance with one embodiment of the invention,

Figure la is a block diagram representing one pair of ground radio transmitter stations of the navigation system which transmit A and B pulses, respectively,

Figure 2 is a block and circuit diagram of the pulse generating unit shown in Fig. 1,

Figure 3 is a view of the adjustable cathode-ray trace appearing on the screen end of the cathode-ray indicator tube that is included in the apparatus of Fig. 1 and of the timing marker pulses thereon which are counted to determine the time interval between the received A and B pulses,

Figure 4 is a view showing the relation of the unblanked portion of the adjustable cathode-ray trace with respect to the horizontal deflecting waves and with respect to the timing marker pulses,

Figure 5 is a group of graphs which are referred to in explaining the operation of the system shown in Fig. 1,

Figure 6 is a circuit diagram of the wave shaping and cathode-ray deflection and control circuits included in the system of Fig. 1, and

Figure 7 is a group of graphs that are referred to in explaining the operation of the circuit shown in Fig. 6.

In the several figures, similar parts are indicated by similar reference characters.

The pulse generator and station selection circuit which will now be described under the headings The pulse generator unit and Count subtraction for station selection is the same as that described and claimed in application Serial No. 552,146, tiled August 3l, 1944, in the name of Earl Schoenfeld and entitled Timing marker and station selection apparatus.

The pulse generator ln Fig. l, the pulse generating circuit for producing the timing marker pulses and for producing the controlling or synchronizing pulses that control the cathode-ray deflection' isY shown in block diagram at the top of the figure. VIt is shown in detail in Fig. 2. Referring to` Figs. l and 2,. the pulse generator comprises a crystal oscillator 10v that produces a sine wave voltage of stable frequency which in the example illustrated is kilocycles per second, the repetition period being l0 microseconds. The frequency of the crystal oscillator output may be increased or decreased slightly by a manual adjustment as indicated at the control knob 11 for obtaining a tine right or left drift of a received pulse on a cathode-ray sweep trace, the rate of drift being slow enough to be useful on fast sweep presentation.

The crystal yoscillator 10 drives a blocking oscillator 12 or the like to produce periodic pulses which, in the present example, also recur at the rate of 100 kc. per second. The repetition period or time interv-al between successive pulses is, therefore, l0 micro-seconds.

The frequency of the 10 ps. pulses is divided by live by means of a suitable frequency divider 13 such as a second blocking oscillator to produce 50 lits. pulses. While specic valuesare being given for the several frequency division steps, the invention is not limited to these particular values. p

The 5.0' its. pulses are applied through a lead 14 t-o a frequency divider 16 of the counter type described in White Patent 2,113,011: lt divides the frequency by two to produce 100 as. pulses. Also, an additional circuitl is providedso that the divider 16 may be made to lose a count for the purpose of obtaining a different selected pulse repetition period.

The divider 16 comprises a counter circuit portion including an input or bucket capacitor 17, a pair of diodes 18- and 1'9, a storage capacitor 21 and a blocking oscillator portion 22.` ln, addition,` it includes a pair of diodes 2-3 andAv 24 associated' with the storage capacitor 21 for the purpose of making the divider 16 lose a count upon the application of a pulse from a conductor 26 as will be eX- plained hereinafter. The blocking oscillator 22 cornprises a vacuum tube 27 and a transformer 28 coupling the plate circuit to the grid circuit. The cathode circuit includes a biasing resistor 29, bypassed by a capacitor 31, and connected `in series with a bleeder resistor 29". A transformer 32 supplies the 100 us. pulses from the divider 16 to a frequency divider 33 which also is of the type which may be made to lose a count The frequency divider 16 operates as follows: Each of the 50` pts. pulses of positive polarity from the lead 14 puts a predetermined charge on the comparatively large capacity storage capacitor 21 as a result of a pulse of current through the comparatively srnall bucket capacitor 17 and through the diode 19,v the capacity of the capacitor 17 being small enough so that capacitor 17 receives full charge before the termination of an applied pulse. At the end of this current pulse, the capacitor 17 is discharged tov ground potential through the diode 1S. The next 50 its. pulse puts an additional current pulse into capacitor 21, thus raising the voltage across capacitor 21 suciently to trigger the blocking oscillator 22 whereby a pulse is produced across the transformer 2S as is well understood inthe art. The pulse thus produced is applied; to the divider 33 with positive polarity. At the same time the blocking oscillator 22 discharges the capacitor 21 to bring it back to ground potential.

The frequency'divider 33 divides the frequency by ve to produce 500tts. pulses. lt includes a counter portion comprising a bucket capacitor 36, a pair of diodes 37 and 38, andY a storage capacitor 39. It also includes a blocking oscillator portion 41 comprising a Vacuum tube 42, a feedback transformer 43, a biasing resistor 44 and a bypass-capacitor 46.

As inthe preceding divider 16, there is provided in the divider 33 a pair of diodes 47 and 48 for subtracting counts. In the divider 33, however, the application of a pulse from a` conductor 49 will subtract one, two or three counts depending upon the position of the station selectionswitch.

The 500 as. pulses are supplied over a conductor l to a frequencyv divider 52 that divides by two to produce 1000 its. pulses. The divider 52 is similar to the divider 16 with the count subtracting diodes omitted.

The 1000 tts. pulses are supplied to a frequency divider 56 that dividesby tive, to produce 5000 as. pulses which, in turn, are supplied to a frequency divider 59 that divides by four to produce 20,000 its. pulses. The dividers 56 and 59 are similar to the divider S2 except for the diierence in circuit constants.

The 20,000 us. pulses may be passed through a clipping circuit 60 and supplied over a conductor 61 to a square wave generator 65 (Fig. l), such as an Eccles-Jordan oscillator for obtaining a square wave having a repetition period of 40,000 its. From this square wave are obtained, by means of suitable wave shaping and delay circuits describedk hereinafter, the desired driving or synchronizing pulses for the horizontal deection.

The 20,000 pts. pulses are also supplied over a conductor 62 and through a bucket capacitor 63 of the rst count subtraction circuit to a station selection switch 64; they are also supplied to the second count subtraction circuit through a coupling or blocking capacitor 66 of large capacity to a second station selection switch 67 which is ganged with the switch 64 as indicated by the broken line 68, the two switches being operated by a knob 65.

At the switch 64, alternate swit-ch contact points are 4 connected to the feedback conductor 26 whereby at these switch point positions the 20,000 Aas. pulses are fed back to the divider 16 to subtract counts. It may be desirable because of distributed or stray leakage in the switch 64 or capacitors 63 to connect its switch arm to ground through a l megohm resistor 55 to permit charges to leak At the switchv 67, the last six contact points are connected in pairs, the three pairs of contact points No. 2-No. 3', No. 4-No. 5 and No. -N-o. 7 being connected through bucketcapacitors 71, 72 and 73, respectively, to the feedback conductor 49 which leads to the second count subtraction circuit. Thus, with switch 67 in any one of the last six positions, 20,000 its. pulses are applied to the divider 33 to subtract counts.

Before discussing in deta-il the operation of the count subtracting circuits for station selection, it may be noted that the desired timing marker pulses are obtained at various points alongA the frequency divider circuit. In the present system, the 10` its. pulses are supplied from the blocking oscillator 12 to an output lead` S1. The 100 as. pulses are supplied to an output lead 87. The 1000 lus. pulses and 20,000 as. pulses are supplied to marker output leads 88 and 90. The marker leads 81, 87, 88 and 90 supply the 10 its. pulses, the 100 as. pulses, the 1000 as. pulses and the 20,000 as. pulses to amixer tube or circuit 129 (Fig. l) andl from the mixer 129 to al vertical deecting plate of a cathode ray tube 116 as described hereinafter. The cathode ray of the tube 116 is deected horizontally by a deflecting wave that is in synchronism with the 40,000 us. square wave from the EcclesJordan oscillator 65 (Fig. l). It is evident that the 40,000- ;ts. horizontal deflection cycle has a fixed time relation to the timing marker pulses. As will be apparent from the following description, the 20,000 as. pulses may be omitted fromthe group of marker pulses supplied to the marker mixer 129, if desired, where the feature of blanking out a portion of the adjustable trace is employed.

Count subtraction for station selection Referring now more particularly to the feature of subtracting counts for the purpose of station selection, specific pulse repetition rates for a plurality of pairs of ground transmitter stations will be referred to by way of example-to aid in explaining the operation.

It will be assumed that the rst pair of ground stations transmit the A pulses with a repetition period of 40,000 lts. and transmit the B pulses with a like repetition period; thaty thesecond pair of ground stations transmit A and E pulses having a repetition period 4of 39,900 us.; that the third pair transmits 39,800 us. pulses; that the fourth pair transmits 39,700 us. pulses, etc. 1t is apparent that for station selection at the receivingv apparatus, the operator must be able to select corresponding repetition periods for the output of the square wave generator 65 which controls the cathode ray deflection cycle; namely, periods of 40,000 as.; 39,900' as.; 39,800 us.; 39,700' les.; 39,600 us.;etc.

It will be notedthat the several repetition periods differ from each other by lus. or by integral multiples thereof, and that this corresponds to repetition periodv ditt'erences of 50 us. or integral multiples thereof at the output of the frequency divider chain, i. e., at the input of the clipper 60. Therefore, the desired repetition period can be obtained by shortening` the 20,000 ps., period by 50 its., by 100 us., by 150 its., etc.

For example, to obtain the 39,900 us. repetition period the switches 64 and 67 are moved to the No. l switch contact points. At this switch position the 20,000 us. pulses from the lead 62 are fed back by way of the bucket capacitor 63, the switch 64 and the conductor 26 to the frequency divider 16 only. Upon the occurrence of a 20,000 as. pulse, it produces a pulse of current through the bucket capacitor 63 and through the diode 23 to add a charge to the storage capacitor 21. At the end of they pulse, the capacitor 63 discharges through the diode 24 to its original potential. By properly selecting the capacity value of the bucket capacitor 63, the added charge isV made equal to the charge which is added to the capacitor 21 by a single 50 us. pulse. Thus, the 20,000 us. pulse causes the blocking oscillator 22 to re one pulse earlier or 50 as. sooner than it normally would whereby the desired repetition period of 19,950 as. at the clipper 60 or 39,900 its. at

the output of @-the- E-J oscillator-h65 g-is.- obtained. It may be noted that, in the example given, each time a 20,000 lits. pulse occurs, the divider 16 divides by one instead of by two. A

To obtain the 39,800 fis. repetition period, the switches 64 and 67 are moved to position No. 2. Now the 20,000 ns. pulses are applied through the. bucket capacitor 71 to the divider V33 and upon the occurrence of a 20,000 ns. pulse it applies a charge to the capacitor 39 through the diode 48. At the end of the pulse the capacitor 71 discharges through the diode 47 yto its original potential. The capacitor 71 is given a capacity value such that this charge applied by the 20,000 lits. pulse is equal to the charge applied bya single 100 fis. pulse. Thus, upon the occurrence of a 20,000 las. pulse the blocking oscillator 41 res one pulse early or 100 its. sooner than it normally would whereby `the desiredl repetition period of 19,900 its. is obtained at the clipper 60 and a repetition period of 39,800'ps. is obtained at the output of the E-J oscillator 65. It may be noted that in the example given, the divider 33 divides byfour instead of by ve upon the occurrence of each' 20,000 ,Us pulse.

To obtain the 39,700 las. repetition period, the switches 64 and 67 are moved to the No. 3 position, this being the switch position shown in the drawing. Now the 20,000 as. pulses are applied to both the divider 16 and the divider 33 through the switches 64 and 67 whereby both dividers lose a count. Specifically, the blocking oscillators 22 and 41 of dividersr16 and 33 fire 50 its. and 100 its. early, respectively, or a totalof 150 its. early. Thus, the desired repetition period of 2 l9,850 lts. or 39,700 as. is obtained at the E-J oscillatorl output.

To obtain the 39,600 ps. repetition period, the switches 64-and 67 are moved to the No. 4 position. `Again the 20,000 ns. pulses are applied to the divider 33 only, but this time through the capacitor 72 which has a capacity value such that a 20,000 ps. pulse causes the divider 33 to lose two counts, i. e., to trigger 200 ps. early. Thus, the desired period of 2X 19,800 its. or 39,600 pas. is obtained at the E-J oscillator.

At the No. 5 switch position, the divider 16 again triggers 50 its. early and the divider 33 triggers 200 ns. early, or a total of 250 its. for the two dividers. Thus, the repetition period is 19,750 ps. at the input to clipper 60 or 39,500 ps. at the output of the E-I oscillator 65.

At the No. 6 switch position, only the divider 33 receives the 20,000 its. pulses. These pulses are applied through the capacitor 73 which is adjusted to make the divider 33 lose three counts. Thus, it triggers 300 its. early to give a repetition period of 2 l9,700 ns. or 39,400 ns. at the E-I oscillator output.

At the No. 7 switch position, both of the dividers 16 and 33 lose counts, divider 16 triggering 50 ,us.-early and divider 33 triggering 300 its. early, or a total of 350 as. early whereby the repetition period is 19,640 its. at the clipper 60 or 39,300 its. at the E-J oscillator Voutp It may be preferred to employ a different group of repetition periods than the group of 40,000 us., 39,900 its., etc., assumed above. By making the nal divider stage 59 divide by three, for example, instead of by four, the divider chain output pulses have a repetition period of 15,000 pts. so that a group of repetition periods of 30,000 its., 29,900 ps., etc. may be ernployed. Or the divider stage 59 may be made to divide by five to obtain a group of repetition periods of 50,000

us., 49,900 lis., etc. l

In order to obtain a more rapid right drift of the A and B pulses in the preliminary steps of obtaining a time diierence reading, it may be desirable to provide a capacitor 95 that may be connected by a switch 96 to the coupling capacitor 66 so that by closing the switch 96 additional counts will be lost by the divider 33. Thus, the A and B pulses may be drifted toward the right by closing the switch 96. When the switch 96 is opened the A and B pulses stop drifting and again are stationary.

Cathode-ray trace cmd timing marker presentation the appearance of the unblanked portion' of theI adjust-4 able cathode ray trace on which the timing marks'are counted to determine the time interval between vthe A and B pulses from a pair of ground stations. It will be noted that 1000 its., ps., and 10 its. markers appear on the trace and that the left-hand portion ofthe trace has been expanded. The marks are counted from right to left, first the 1000 its. marks, then the 100 lits. marks, then the l0 its. marks, and nally the number of 1 lits. units are estimated. In the exampleshown the reading is 3547 its.

As shown in Fig. 5, the B pulse is the'pne thatfoccurs after the mid-point of the A pulse period, and it is the A pulse that is made to fall on the adjustable detlecting wave trace. By making the A pulse fall on the trace having the adjustable startingitim'e`it;is possible to provide an expanded trace with the expansion occurring where it is needed, i. e., where the'lQps. markers are to be counted. broadly in copending application Serial No. 560,648,' fi1ed October 27, 1944, in the name of; George D. Huls,t,lr.,

entitled Radio navigation system now Patent 2,430,570 issued November ll, 1947 and describing a systemrwherein timing marks are counted on two traces, only one .of which is expanded. In the present simplified system, all timing mark counting is done on only one trace.

In Figs. 4 and 5, the graphs F and B show the ,wave shapes of the horizontal deflecting wave and of the blankng wave, respectively, for obtaining the desired cathode ray traces. The starting time t of the second saw-tooth Wave c-d of the horizontal deecting wave.' F may be adjusted by adjusting a multivibrator 101 bya knob 102 (Fig. 1) as will be explained hereinafter, thus adjusting the starting time of the second saw-tooth wave trace shown in Fig. 3. The right-hand portion of the second saw-tooth wave c-d is blanked out from the mid-point of the deilecting wave cycle by the blankng wave B.

Referring to Figs. 4 and 5, the received pulses B and A from the selected pair of stations are caused to appear on the rst and second traces a-bv and c-d, respectively, at their expanded ends. This is accomplished by first making the pulses A and B stay stationary on the two sweeps by making a crystal oscillator frequency` adjustment at the knob 11 in the event that there is a slight drift of these A and B pulses. pulses are now brought into the position of alignment or coincidence (i. e., one pulse above the other onV the cathode ray tube screen) by the following procedure.

By adjustment of the crystal oscillator frequency at the knob 11 and/or by moving the station selection switch knob 65 to obtain a different pulse repetition rate, the pulse B is drifted onto the expanded end of thetrace'ab. Next, the pulse A is brought onto the expanded end ofy the adjustable trace cd and is brought into coincidence with the pulse B. In order to bring the pulse A into coincidence with the pulse B, the starting time t of the second sweep of the horizontal deflection wave F (Figs. 4 and 5) is'a'djusted by adjusting the multivibrator 101 at the knob 102', tlie circuit for accomplishing this being described hereina ter.

A comparison of the A and B pulses as shownin'Fig. 5 with the horizontal deflecting wave F of the same gur'e will show that the condition of coincidence of the'pulses A and B has been illustrated, both pulses falling on the expanded ends of successive traces and occurring at equal time intervals from the starts of the traces. It will be understood that while the pulses A and B and their corresponding traces appear alternately on the cathode raytube screen, they appear to the eye to occur simultaneously because of persistence of vision, lagof phosphorescence of the screen or both. Y

Although the A and B pulses and the timing marks may be made to appear on the cathode ray traces simultaneously, it is usually preferred that the A and B pulses onlyl appear on the sweep traces during the alignment step and that only the timing marks appear during the time reading step. The following description assumes that the latter is accomplished by means of suitable switching de'- scribed hereinafter.

After the pulses A and B have been aligned, the operator moves a switch 126 (Fig. 1) from its alignment posi-v tion to a time reading position. The timing marker pulses now appear on the unblanked portion c-d' of lthehsweep trace c-d as shown in Figs. 3 and` 4, and, by counting thel 1000ps., the 100 ns., and the lofts. timing marks, the dei r www This ,feature `is claimed The A and B- sired time diierence bet-weert the pulses A and B can be avoided.

From the foregoing discussion, it will be apparent that the amount that the starting time t of the second sweep portion c-d of graph F (Figs. 4 and 5) has to be shifted from the center or 20,000- its. position in orden to bring the pulse A into coincidence with the pulse B is a measure of the time difference between the pulses A and B or, in the example mentioned, it is a measure of the amountr that an A pulse is away from the midpoint of the repetition period of the B pulses.

General' description of cathode-ray trace producing circuits I he circuit for obtainingthe operation described in connection with Figs. 3, 4 and 5 will rst be described generally with reference to the block diagram of Fig. 1 and the graphs of Fig. 5.

Referring to Figs. l and 5, the Eccles-Jordan oscillator 6W5, is l'iggered by the 20,000 ns. pulses supplied over the conductor 61 to produce a rectangular voltage wave B' which is derentiated by differentiating circuits 106 and 107 to produce similar waves C and C', respectively. The positive pulse portions of the wave C trigger the multivibrator 101 to produce the rectangular wave D. The timing of the back edge of the narrow pulse portion of the wave D is adjustable by means of the knob 102', this timing of the back edge controlling the starting time t of the second sweep portion of the deflecting wave AF as will soon be apparent. several well known types such as, for example, Vthe one described in British Patent 456,840 to White and in the A. I. E. E. for June 1941, vol. 60, pp. 371-376.

The rectangular wave D from the multivibrator 101 is passed through a differentiating circuit 108 to produce the wave E which is supplied over a conductor 109 and through a mixer tube or circuit 110 to a deflecting wave producing circuit 111. The wave C is also suppiied over a conductor 112 and through the mixer 110 to the deecting circuit 111 whereby the positive pulses of the wave C and of the wave E initiate the rst and second sweeps, respectively, of the horizontal deflecting wave F. The deflecting wave F is applied from the circuit 111 through a push-pull amplifier 113 to the horizontal deilecting plates 114 of the cathode-ray indicator tube 116. The circuit 111 will be described in detail hereinafter with reference to Fig. 6.

Separation of the two cathode ray traces produced by the rst sweep portion a-b and the second s weep portion c-d, respectively, of the deccting wave F is obtained by applying the wave D over a conductor 124 to the lower vrticalldeecting plate 117- After aligning. the pulses. A and B, rio use is"made of the trace produced by the first sweep a-.b and it could be blanked out during the counting of the time markers although this is not done in the example illustrated.

To make a time measurement, the operator throws a switch 126 comprising switch arms 126:1 and 126b iirst to a pulse alignment position for aligning the pulses A and B received from a pair of ground transmitters, and then, after the pulse alignment, throws it to a time marker reading position (the switch position illustrated in Fig, 1 to count time marker pulses. In the align position of switch 126, a radio receiver 127 Supplies the A and B pulses of a pair of ground stations over a conductor 112,55 to the upper vertical deflecting plate 117. The receiver 127 is tuned to the carrier wave frequency common to one whole group of transmitter ground stations of the navigation system, station selection being by means of the different pulse repetition rates for different pairs of stations as previously described.

In the time marker read position of switch 126, the time marker pulses of lOns., lOOns., and 1000ps. repetition periods are supplied from the mixer tube 129 over a conductor 131 to the upper vertical deecting plate 117, the A and B pulses no longer being applied to the cathode ray tube 116. The 20,000,us. pulses may also be included in this group of marker pulses, particularly if the feature of blanking out a portion of the adjustable trace is not employed. At the same time the wave Bf is applied as a blanking pulse from the E-J oscillator 65 through a conductor 118, and through the switch arm 126a and a blocking capacitor 122 to the control grid 119 of the cathode ray tube 116. A suitable operating bias is supplied to the grid 119 through a grid resistor 120.

The multivibrator 101 may be any one of 8 Dierential gain control circuit A diterential gain control circuit for the receiver 1 27 preferably is provided as indicated in Fig. l for thepurpose of 4keeping the amplitudes of the A and B pulses substantially alike at the receiver output, thus facilitating the A and B pulse alignment. The gain control circuit includes a potentiometer resistor 171 The wave D is applied to the opposite endsi of the resistor 171 with opposite polarities, a wave D of reversed polarity being obtained by means of a polarity reversing tube 123. An adjustable tap 172 may be' moved to either side of the center of resistor 171 to decrease the gain of the receiver 127 during either the reception of the pulse A or the pulse B. As this circuit forms no part of the present invention no detailed description will be given. It may be noted that the differential gain control circuit may be the same as that described in application Serial No, 560,648, filed October 27, 1,9 44 by George D.V Hulst, Jr. and entitled Radio navigation system.

Detailed description of deflecting circuit (Figure 6) Referring to Fig. 6, the multivibrator 101, in the example illustrated, comprises two triodes 132 and 133 which are connected to form a cathode-coupled multivibrator. The pulses C from the differentiating circuit 106 are applied to the grid of the triode 132, this grid having an adjustable positive bias applied thereto from a potentiometer resistor 1 02 through a grid resistor 134. This bias is adjusted by means of the control knob 102 operating an adjustable tap on resistor 102 for adjusting the timeof occurrence of the back edge of the narrow multivibrator pulse of the wave E. Preferably a bypass capacitor is connected from the adjustable tap to ground. The differentiating circuit 10,6 comprises a small coupling capacitor 136 and the grid resistor 134.

The ditferentiating circuit 107 applies the pulses C` to the grid of a triode A that forms part of the mixing circuit 110. The differentiating circuit 107 compr-ises a small coupling capacitor 137 and a grid resistor 138. The differentiating circuit 103 applies the pulses E to the grid of a triode 110B forming the other part of the mixer 110, the tube 110A and 110B having a common cathode resistor 1,39 across which the mixed signals C and appear.- The differentiating circuit 108 comprises a small coupling capacitor 141 and a grid resistor 142.

The mixed signals C and E. preferably are applied through a clipper diode 143 to keep the amplitude of the positive pulses a constant value. The clipped pulses re6 applied to the grids of a pair of triodes 144 and The triodes 144 and 146 have wave-shaping cathode circuits 147 and 148, respectively. The circuit 147 comprises a cathode resistor 149 and a capacitor 151 in parallel therewith. The circuit 1 48 comprises a cathode resistor 152Halnd a capacitor 153 in parallel therewith.

Upon the occurrence of either a pulse C or a pulse E, the tubes 144 and 1.46 which are normally biased to cutoff, conduct anode current to charge the capacitors 151 and 153, respectively, rlfhis charging of 151 and 153 is practically instantaneous.` At lthe termination of the pulse C or E, the capacitors 151 and 153 discharge at a rate that is slow compared with the charging rate and at a rateA that is determined by the time constants of the circuits 1,47 and 148, these time constants differing from each other. Thus, asvillustrated in Fig. 7, across the circuits 147 and 148 there are produced the voltage waves x and y, respectively, which are to be combined with a third voltage wave r to produce the desired logarithmic deecting Wave F.

The wave z is obtained by applying the pulses C and E from the cathode resistor 139 over a conductor 154 to the grid of a tube 156 which includes a wave shaping network 157 in its cathode circuit. The network 157 comprises a high impedance resistor 158, the lower portion of a biasing resistor 159, and a capacitor 161. As in the wave-shaping circuits for producing the Waves x and y, the Capacitor 161 is charged rapidly upon application of a pulse to the tube 156. To produce wave z, however, the discharge of capacitor 1,61 is made slow enough by proper adjustment of the time constant of network 157 so. that i@ (unlike capacitors 1.51 and .153) has not. discharged coinpletely by the time` the next pulse C or E occurs.V The' Wave g is applied to a cathode follower tube 160.

.the deectingwave is alinear sawtoot'h wave. -viouslyindicated,lthe invention may kbe, ipracticedwithout the blanking feature by including the 20,000. its. pulses It will be seen that the effect of adding the waves x and. y..to the.Wavefz-:isf-tol-greatlywincrease the slope of the dcflecting wave F at itsstart whereby the scale for the corresponding portion of the lcathode-ray trace is expanded. The waves x, y and z are added by supplying them through leads 162,.;.1631-.and 164 to the input circuit ofthe deiiecting-wave amplifier 113. T he leads 163 and-164 preferably include high impedance resistors 166 and 167 shunted by capacitors 168v and 169, respectively, for obtaining undistorted addition of the several Waves. .It will begapparent that the detiecting wave F may be shaped as desired for different scale expansions by changing the time constants of one or more of the circuits A147, 148,and.157.

In Fig. 6, circuit valueshave been indicated in ohms, thousands of ohms, megohms, microfarads and micromicrofarads merely by way :of example.

It should be understood that the invention is not limited to the use of the speciiicnlogarithmic deiiectiug .,wave circuitdescribed above and, in fact, is not limited to the use of kadelecting wave that is logarithmic in wave form since other waves such as an exponential ...shaped deecting wave mayfbezused for obtaining an expanded. trace. .limited to the use of an-expanded trace. since, for ex- In yone aspect, the invention is not ample, the blanking ,featurel may be employed `where Asprein the group of marker pulses -supplied lto the marker .mixer 129. Then a 20,000 its. timing mark will appear lon the adjustable trace c-d, this mark-being easily identified-since it is themark'. of the largeStamPIitude, and `the timing marks to the left-of the 20,000 *,us. mark are 4counted f as previouslyy described.

4The-scope ofthe `invention is set forth in the appended claims.

We claim as our invention: f

. 1. In a navigation ,system wherein periodically recurring radio pulses are transmitted from A and B ground stations to radiate A andB pulses with the B pulses occurring at aipredetermined time .following themidpoint of the period of the A pulses, receiving apparatus for measuring the time interval between the A and B'. pulses at a point remote from said ground stations lkwhichcomprises means for. receiving said A and B` pulses .at'said point, meansl for producing successively pairs of sequentially occurring deflecting waves having decreasing slope from the start of the wave andwhich are identical throughout their useful deflecting portions, each pair of Awaves'having a total repetition period equal to that of said A and B pulses, the second wavev of a pair starting before the mid-point of said period andendingafter said mid-point, -ineans for producing timing pulses having a xed time relation to the start and nish of said repetition period, means for'` causing each of said detiecting 'wavesto produce a cathode-ray trace-and means for causing said A andv B pulses to appear on said two cathode-ray traces, respectively, with the A pulse on the trace that is produced by the second wave of A the pair of waves, means vfor changing the starting time of saidV second deecting waveV with respect to said mid-point until said A and B pulses on said traces are in alignment or'coincidence, and means for causing saidtiming pulses to'appear as timing marks on the trace producedfby said second wave. y n y `2. In a navigation'system wherein periodically `recurring radio pulses 'are transmitted from Aand B ground stations'to radiate A and B pulses withthe B pulses occurring at a predetermined time following the midpoint'of vthe vperiod of the A pulses, the vmethod of measuring the time interval between the A and B pulses at a point remote from'said ground stations which comprises'receiving said A and B pulses at said point, producing successivelypairs of sequentiallyV occurringv -deiecting waves having decreasing slope from the startof the wave for expanding their jcathode-ray traces, said waves being identicalf`thougliut"'their useful deliectng portions, each pair of waves having a total repetition period equal to that of said A and B pulses, the second wave of a pair starting before the mid-point of said period and ending after said mid-point, producing timing pulses having a fixed time relation to the start and finish of said repetition period, causing each of said deflecting waves to produce a cathode-ray trace and causing said A and B pulses to appear on said two cathode-ray traces, respectively, with the A pulse on the trace that is produced by the second wave of the pair of waves, changing the starting time of said second deflecting wave with respect to said mid-point until said A and B pulses on said traces are in alignment or coincidence, and causing said timing pulses to appear as timing marks on the trace produced by said second wave.

3. In a navigation system wherein periodically recurring radio pulses are transmitted from A and B ground stations to radiate A and B pulses with the B pulses occurring at a predetermined time following the midpoint of the period of the A pulses, receiving apparatus for measuring the time interval between the lA and B pulses at a point remote from said ground stations which comprises means for receiving said A and B pulses-at said point, means for producing successively pairs of sequentially occurring defiecting waves which are substantially logarithmic in wave form and which are identical throughout their useful detlecting portions, each pair of waves having a total repetition period equal to that of said A and B pulses, the second wave of a pair starting before the mid-point of said period and ending after said mid-point, means for producing groups of timing pulses having a iixed time relation to the start and Vfinish of said repetition period and having afdecirnal relation to each other, means for causing each of said deiiecting waves to produce a cathode-ray trace and means for causing said A and B pulses to appear on said two cathoderay traces, respectively, with the A pulse on the trace that is produced by the second wave of the pair of Waves, means for changing the starting time of said second defiecting wave with respect to said mid-point until said A and B pulses on said traces are in alignment or coincidence, and means for causing said timing pulses to appear as timing marks on the trace produced by said second wave.

4. In a navigation system wherein periodically recurring radio pulses are transmitted from A and B ground stations to radiate A and B pulses with the B pulses occurring at a predetermined time following the mid-point of the period of the A pulses, the method of measuring the time interval between the A and B pulses at a point remote from said ground stations which comprises receiving said A and B pulses at said point, producing successively pairs of sequentially occurring deflecting waves, each of said pairs Lof wavesdeining a deflecting wave cycle, deiiecting a cathode `ray Vby said waves to produce two cathode-ray traces, causing said A and B pulses to appear on said two traces with the A pulse on the trace that is produced by the second of said pair of deflecting waves, adjusting the starting time of the second of said pair of deflecting Waves until it is such that said A and B pulses are aligned, producing timing marks on the trace produced by said second deflecting wave, and blanking out the portion of said last trace from the mid-point of said deliecting wave cycle to the end of said cycle.

5. In a navigation ksystem wherein periodically recurring radio pulses are transmitted from A and B ground stations to radiate A and B pulses with` theB pulses occurring at a predetermined time following the mid-point of the period of the A pulses, the method of measuring the time interval between the A and B pulses at a point remote from said ground stations which comprises receivingsaid A and B pulses at said point, producing successively pairs of sequentially occurring deflecting waves having decreasing slope from at least near the start of the wave which are identical throughout their` useful' deflecting portions, each of said pair of waves defining a deflecting wave cycle, deiiecting a cathode ray by said Waves to produce two parallelL adjacent cathode-ray traces, causing said A and B pulses to appear on said two traces with the A pulse on the trace that is produced by the` second of said pair of deflecting. waves, adjusting the starting time ofthe second of ,said pairof deflectingwaves until it lis such that `said A and B pulses are aligned, producing timing marks on the trace produced by said second deflecting wave, and blanking out the portion of said last trace from the mid-point of said deflecting wave cycle to the end of said cycle.

6. In a navigation system wherein periodically recurring radio pulses are transmitted from A and B ground stations to radiate A and B pulses with the B pulses occurring at a predetermined time following the mid-point of the period of the A pulses, means for measuring the time interval between the A and B pulses at a point remote from said ground stations which comprises means for receiving said A and B pulses at said point, means for producing successively pairs of sequentially occurring deflecting waves, each of said pairs of waves defining a deecting wave cycle, means for deflecting a cathode-ray by said waves to produce two cathode-ray traces, means for causing said A and B pulses to appear on said two traces with the A pulse on the trace that is produced by the second of said pair of deflecting waves, means for adjusting the starting time of the second of said pair of detiecting waves until it is such that said A and B pulses are aligned, means for producing timing marks on the trace produced by said second deflecting wave, and means for blanking out the portion of said last trace from the mid-point of said delecting wave cycle to the end of said cycle.

7. The method of measuring the time relation of one group of periodically recurring received pulses with respect to another group of periodically recurring received pulses where both groups of pulses have the same repetition period, said method comprising the steps of producing two successive cathode-ray deecting waves each starting from the same voltage level and each of identical slope over the useful deecting portion, the second of said waves having an adjustable starting time, said pair of waves having a total repetition period equal to that of said groups of received pulses, producing timing pulses having a Xed time relation to the start and iinish of the cycle of said two deecting waves, causing each of said deflecting waves to produce a cathode-ray trace and causing a pulse of each group of received pulses to appear on said two cathode-ray traces, respectively, changing the start of the second deflecting wave of said cycle with respect to the mid-point of the full deflecting wave cycle until said pulses on said`traces are in alignment or coincidence, causing said timing pulses to appear as timing marks on said traces, and blanking out said second deflecting wave from said mid-point to the end of said cycle whereby the timing marks on the remaining trace produced by said second deecting wave indicate the amount of time that the "start of said second deecting wave is shifted with respect to said mid-point of the full deflecting wave cycle.

8. In a system for measuring the time relation of one group of periodically recurring received pulses with respect to another group of periodically recurring received pulses where both groups of pulses have the same repetition period, said system comprising means for producing two successive cathode-ray deflecting waves each starting from the same voltage level and each of identical slope` over the useful deflecting portion, the second of said waves having an adjustable starting time, said pair of waves having a total repetition period equal to that of said groups of received pulses, means for producing timing pulses having a fixed time relation to the start and finish of the cycle of said two deecting waves, means for causing each of said deecting waves to produce a cathode-ray trace and means for causing a pulse of each group of received pulses to appear on said two cathode-ray traces, respectively, means for changing the start of the second deflecting wave of said 'cycle with respect to the mid-point of the full deecting wave cycle until said pulses on said traces are in alignment or coincidence, means for causing said timing pulses to appear as timing marks on said traces, and means for blanking out said second deecting wave from said midpoint to the end of said cycle whereby the timing marks on the remaining trace produced by said second deflecting wave indicate the amount of time that the start of said second deliecting wave is shifted with respect to said mid-point of the full deliecting wave cycle.

9. In a navigation system wherein periodically recurring radio pulses are transmitted from A and B ground stations to radiate .A and B pulses with the B pulses occurring at a predetermined time following the 12 mid-point'of the period of the A pulses, receiving apparatus for measuring the time interval between the A and B pulses at a point remote from said ground stations comprising means for receiving said A and B pulses at said point, means for producing successively pairs of sequentially occurring deecting waves which are iden tical throughout their useful deecting portions, `each pair of waves having a total repetition period equal to that of said A and B pulses, means for producing timing pulses having a fixed time relation to the start and finish of the cycle of said two deecting waves, means for causing each of said deflecting waves to produce a cathode-ray trace and means for causing said A and B pulses to appear on said two cathode-ray traces, respectively, with the A pulse on the trace that is produced by the second wave of the pair of waves, means for changing the starting time of said second deecting wave with respect to the mid-point of the full deflecting wave cycle until said A and B pulses on said traces are in alignment or coincidence, means for causing said timing pulses to appear as timing marks on said traces, and means for blanking out said second deflecting wave trace from said mid-point to the end of said cycle whereby the timing marks on the remaining portion of the second deflecting wave trace indicate the amount of time that the start of said second deecting wave is shifted with respect to said midpoint of the full deflecting wave cycle.

l0. In a navigation system wherein periodically rccurring radio pulses are transmitted from A and ground stations to radiate A and B pulses with the B pulses occurring at a predetermined time following the mid-point of the period of the A pulses, receiving apparatus for measuring the time interval between the A and B pulses at a point remote from said ground stations which comprises means for receiving said A and B pulses at said point, means for producing successively pairs of sequentially occurring deflecting waves having decreasing slope from the start of the wave and which are identical throughout their useful deflecting portions, each pair of waves having a total repetition period equal to that of said A and B pulses, the second wave of a pair starting before the mid-point of said period and ending after said mid-point, means for causing each of said deecting waves to produce a cathode-ray trace and means for causing said A and B pulses to appear on said two cathode-ray traces, respectively, with the A pulse on the trace that is produced by the second wave of the pair of waves, and means for changing the starting time of said second deflecting wave with respect to said mid-point until said A and B pulses on said traces are in alignment or coincidence.

l1. ln a navigation system wherein periodically recurring radio pulses are transmitted from A. and B ground stations to radiate A and B pulses with the B pulses occurring at a predetermined time following the mid-point of the period of the A pulses, the method of measuring the time interval between the A and B pulses at a point remote from said ground stations which comprises receiving said A and B pulses at said point, producing successively pairs of sequentially occurring deecting waves having decreasing slope from the start of the wave for expanding their cathode-ray traces, said waves being identical throughout their useful deflecting portions, each pair of waves having a total repetition period equal to that of said A and B pulses, the second wave of a pair starting before the mid-point of said period and ending after said mid-point, causing each of said deecting waves to produce a cathode-ray trace and causing said A and B pulses to appear on said two cathode-ray traces, respectively, with the A pulse on the trace that is produced by the second wave of the pair of waves, and changing the starting time of said second deflecting wave with respect to said mid-point until said A and B pulses on said traces are in alignment or coincidence.

No references cited. 

